Process for separation of highenergy propellant oxidizers



A ril 2, 1968 H. BIEBER ETAL 3,376,318

PROCESS FOR SEPARATION OF HIGH-ENERGY PROPBLLANT OXIDIZERS Filed March 9, 1962' 2 Sheets-Sheet 1 RAFFINATE 2 u 1| 1| L' T Li HEAVY FEED SOLVENT s 7 7 7 3 EXTRACTA 9 EXTRACTORS 5 FIG 2 B INCREASES WITH TETRAKIS CONTRATIOI?25 THEORY PREDICTS SEPARATION a l I 1 U) m2o 20 LSIO a: w 0.5 u. u. u. E I I5 o 5 9... CL 0 1: I I0 p 5 IO 5 Mole Ratio Of a? o 5 Tetrukis To Bus In Feed 5 5 Is Parameter -I m o I l I l o I I B= K'l/Kb NUMBER OF THEORETICAL STAGES F l G.- 6 FIG 7 Potent Afiorn ey April 1963 H. BIEBER ETAL 3,376,318

PROCESS FOR SEPARATION OF HIGH-ENERGY PROPELLANT OXIDIZERS Filed March 9, 1962 2 Sheets-Sheet 2 a|s(-|= TETRAK|$(NF2) T=25C. T= 25c.

H DH PDH FIG.-2 FIG-3 K DECREASES Ki INCREASES I l I l 1 I I I ols 05 I I l l I l l l o :0 20 so 40 so 0 IO 20 MOLE as m H PHASE MOLE TETRAKIS m H PHASE FlG.-4 FIG- 5 Hermon Bieber Hurry M.Tc|ylor Inventors Lawrence Spenudel y M Patent Attorney United States Patent 3,376,318 PROCESS FOR SEPARATION OF HIGH- ENERGY PROPELLANT OXIDI-ZERS Herman Bieber, Kenilworth, N.J'., Harry M. Taylor, New

Yorlr, N.Y., and Lawrence Spenatlel', Fanwood, N.J.,

assignors. to Esso Research and Engineering Company,

a corporation of Delaware;

Filed Mar. 9, 1962, Ser. No. 179,522 4 Claims. (Cl. 260, 347.7)

This invention relates to a method of separating by liquid-liquid extraction a difluoramino organic compound having a higher number of NF groups from a mixture thereof with a compound containing fewer NF groups in the molecule. The NF- groups are linked to carbons, and herein these difluoramino organic compounds are termed CNF compounds.

With synthesis of relatively high molecular weight, low volatility, CNF compounds, e.g. those containing 4 to 12 or more carbon atoms per molecule, larger scale separation of such compounds, especially from mixtures of compounds with. similar carbon structures according to their CNF content, has become a difficult problem. Fractional distillation under vacuum has its limitations and is often not feasible. Gas chromatography has lessened value for separation of lowvolatility liquid and solid compounds and for larger scale operations. Moreover, partition chromatography in the conventional manner has given difiiculties in separation when a suitable solid adsorbent was not used, and when the rate of flow is not extremely slow.

Now, in accordance with the present invention, a liquidliquid extraction technique with proper solvents is provided for etficient separation of CNF compounds of relatively low volatility based on preferential solvent action for CNF compounds of higher NF content by a liquid halocar-bon solvent which is not miscible with a hydrocarbon liquid that preferentially dissolves the CNF compound of lower NF content.

In the synthesis of many CNF compounds, mixtures are obtained of the derivatives containing varying numbers of NF groups linked to carbon atoms. The organic compoundused as a reactant in the synthesis of the CNF compounds maybe an olefin, diolefin, triolefin, unsatu rated cyclic ethers, cycloalkadienes, and aromatic hydrocarbons, and such compounds containing halogen substituents or other functional groups. In the reactions of such compounds with N 11, NF groups add to one or more double bonds to form mono-(NF bis-( NF tris- (NF tetrakis-(NF and pentakis-(NF and higher adducts. In some, NF groups are substituted for hydrogen, halogen or other reactive atom or functional group.

An example of a product mixture requiring isolationv or concentration of QNF components having-higher energy value (higher NF content is amixture of. terakis- (NF )-tetrahydrofuran with the bis-(N1 furanadduct, bis-(NF )-dihydrofur-an.

r N J NF J NIE tetrakis bis Similarly, there are many other product mixtures for which the liquid-liquidextraction; treatment is appropriate for isolating or concentrating the components having higher NF content, e.g. components having 4 or more NF groups per molecule from. components having fewer NF groups per molecule. Examples of such mixtures are: (1) a mixture of pentakis-(NF pentane withmono-(NF bis-(N1 and tris-(NF derivatives. of l,5,-iodo-2,3-pentadiene; (2) tetrakis-(NF butane with bis-(NF bu.-

tone; (3) pentakis-(NF and tetrakis-(NF derivatives of cyclohexadiene mixed with lower NF adducts and substitution derivatives of cyclohexadiene; ('4) mixtures derived from reaction of benzene with N F4.

The preferred liquid-liquid extraction method for separating the components of a mixture with respect to their CNF group contents utilizes a double solvent in a multistage countercurrent system. Each of the two solvents employed should have low solubility for the other. One of the solvents, characterized by benzene, a liquid hydrocarbon, or similar organic compound of relatively low dielectric constant (eg. a dielectric constant in the range of about 1.8 to 2.5), has a preferential solubility for the components of low NF group contents. The other solvent, which is more polar, such as a polyhalogenated hydrocarbon, has preferential solubility for the components of higher NF group contents. Each of the solvents. must be separable from the solutes, as by distillation.

As a model extraction system chosen for demonstrating the invention, a mixture of bis-(NF and tetrakiS-(NF adducts was used with the solvent pair of benzene and perfiuoro 3,4-dimethylhexane (PDH). A Craig multistage extractor like, that described in Technique of Organic Chemistry, vol. III, p. 285, (1950), Interscience was used.

A method for determining proper solvents for obtain ing satisfactory separation of the mixed NF adducts involves first determining the distribution coefficient for each of the solute components in, the two solvents with variation of the concentration of the solute component. The distribution coefiicient may be expressed: as the ratio of the concentration of the particular solute component in each of the separate solvent phases. Thus, the distribution coefiicient for the bis-(NF furan adduct is:

bis adduct in PDH phase bis adductin benzene phase The distribution coeflicient for the tetrakis-(NF' furan adduct-is:

tetrakis adduct in PDH phase tetrakis adduct inbenzene phase The separation factor or selectivity can then be determined for various concentrations of the solute components in one phase and the varying moleratios of the solute components in the feed mixture. The separation factor or selectivity is:

By using the solubility relationships thus determined, the number of theoretical stages required for a desired degree of'separation can readily be calculated for any feed composition, provided there are no characteristics which alter the relationships, e.g. interactions of the solutes in the solvents. No such interactions were found and the experimental data agreed quite well with the predicted separation. The technique used: for determining suitablesolvent pairs and for carrying out the separation will be described in reference to the drawings, wherein:

FIGURE 1 is a schematic showing. of-a multistageextractor. for continuous. countercurrent flow. of the solvents and their extracts;

FIGURE 2 is. a. ternary. equilibrium diagramv for the system of bis-(N13). furanv adductv with the solvent pair, e e an PDH;

FIGURE 3 is the ternaryequilibrium diagramfor the system of tetrakis-(NF- furan adduct with the solvent pair, benzene and PDH;

FIGURE 4 shows. the relationship of, K to the con centration of the bis. adduct in the benzenephase;

FIGURE 5 shows the relationship of K, to the con.- centration of the tetrakis adduct in the benzene phase;

FIGURE 6 shows the relationship of the separation factor to the concentration of the tetrakis adduct in the benzene phase for varying mole ratios of the solute components;

FIGURE 7 shows the number of stages required in a multistage separation using the double solvent for a given mixture of the solute components to be separated.

The FIGURE 1 extractor is shown to comprise a number of interconnected units, as provided, with a mixing or equilibration zone or chamber 1, a decanting zone 2, and a settling zone 3. The heavier solvent, e.g. the PDH, which preferentially extracts the tetrakis-(NF furan adduct, may be passed by line 4 into the mixing zone 1 of a terminal unit 5, from which the raffinate (bis adduct in the benzene solvent) is decanted through line 6. The settled extract of tetrakis-(NF adduct and the PDH layer is made to pass countercurrently in through lines 7 to the mixing zone 1 of the preceding unit and, similarly, from each settling zone in the mixing zone of a preceding unit, until the extract is withdrawn through line 8 from an end unit 9. The feed of the mixed bisand tetrakis-(NF adductsvin benzene is led into the mixing zone of one of the units, such as the final unit 9 through line 10. The rafiinate of the bis adduct concentrated in the benzene layer, which is decanted in each of the units, is passed by lines 11 to the mixing zone of each following unit and the final rafiinate is withdrawn through line 6. The final rafiinate may be passed to a fractionator for stripping 01f the benzene. The final extract withdrawn through line 8 is passed to another fractionator or stripping zone for separating the tetrakis- (NF adduct from the PDH.

As shown in FIGURE 2, the bis-(NF adduct has a low solubility in the PDH relative to its solubility in the benzene, and the distribution coefiicient, K decreases as the concentration of the bis adduct is increased in the benzene phase. This relationship is indicated by the tielines in FIGURE 2. The concentration of the his adduct in the benzene phase is indicated for one end of the tieline, R, while the concentration of the his adduct in the PDH phase or extract phase is at the other end of the tieline, or point E. The change in K with concentration of the his adduct in the benzene phase is given in the following table: TABLE I.BIS-(NF- ADDUCT OF FURAN EQUILIBRIUM PDH/BENZENE LIQUID PHASE Mole percent bis-(NF adduct in benzene phase:

As shown in FIGURES 3 and 4, the tetrakis-(NF- adduct has a much greater solubility in the liquid PDH phase with increasing concentration inrthe benzene phase, yet has a lower solubility than the his adduct in the benzene phase. These relationships are further brought out by the data in the following table:

TABLE IL-PARTITION COEFFICIENT FOR TETRAKIS- (NFQ) FURAN ADDUCT- Mole percent tetrakis-(NF adduct in benzene phase:

In FIGURE 6 it is shown that with increased concentration of the .tetrakis(NF furan adduct in the feed, the separation of the tetIakis-(NF adduct by extraction into the PDH liquid phase is increased. It will be noted that the selectivity increases as K decreases, and K, decreases as the mole ratio of the tetrakis to the his component decreases, or concentration of his in the benzene increases.

FIGURE 7 shows the number of stages of extraction for any given mole ratio of the his adduct to the tetrakis adduct to be left in the rafiinate. The number of theoretical stages required for this can be calculated for a given feed, given rafiinate solvent, and given extract solvent. In FIGURE 7, benzene and PDH are the solvents. The feed is 32 mole percent bis, 21.8 mole percent tetrakis, and 46.2 mole percent benzene. It is thus indicated that for increased separation efiiciency, the concentration of the tetrakis adduct should be increased both with respect to the concentration of the his adduct and the amount of benzene.

The separation efliciency is the percent of theoretical separation obtained and is dependent on the concentration of the tetrakis-(NF adduct with respect to the bis- (NF adduct in the benzene phase, and also on the use of a suitable mixing time to obtain equilibrium, as shown in the following table:

TABLE III.FACTORS IN SEPARATION EFFICIENCY The technique that has been described can be applied using a relatively nonpolar hydrocarbon liquid solvent for dissolving the solute component of lower NF group content in equilibrium with the more polar polyhalogen or periluoro carbon liquid solvents which preferentially dissolve the compounds of higher NF; content, generally when each of said solute components has the same number of carbon atoms or carbon-containing structure.

What is claimed is:

1. The method of separating CNF organic compounds having a higher number of NF groups from said compounds having a lower number of NF groups by liquidliquid extraction which comprises, contacting the mixture of CNF compounds with a liquid hydrocarbon solvent having a low dielectric constant in the range of about 1.3 to 2.5 which dissolves preferentially the CNF compounds having a lower number of NE, groups, and simultaneously contacting said mixture of CNF compounds with a polyhalogenated organic compound which is more polar than and immiscible with the liquid hydrocarbon solvent and which preferentially extracts the CNF compounds of higher proportion of NF groups, mixing the solutions of said solvents with the CNF compounds dissolved in each of the solvents to obtain substantially an equilibrium distribution, then separating the resulting extract solution of CNF compound containing a higher proportion of the NF groups item the resulting raffinate phase 'of CNF compounds of low NF: group content in the hydrocarbon solvent.

2. The method of separating a CNF- organic compound having .a higher number of NF groups attached to its carbon constituents from a CNF organic compound having a lower number of NF; groups attached to its carbon constituents using a liquid-liquid extraction, said CNF compounds being CNF adducts of an organic compound containing double bonds and 4 to 12 carbon atoms per molecule, which comprises contacting a mixture of the CNF compounds with a liquid hydrocarbon solvent having a dielectric constant number of about 1.8 to 2.5 to dissolve the CNF compounds, contacting the liquidhydrocarbon solution of the CNF compounds with a polyhalogenated organic compound solvent which is more polar than the liquid hydrocarbon solvent and immiscible therewith to preferentially extract the CNF compound having a higher number of NF groups in the polyhalogenated organic compound, mixing the solutions of said solvents with the CNF compounds dissolved in each of the solvents to obtain a distribution of the CNF compounds,

separating a resulting extract solution of the CNF compound having a higher number of NF groups dissolved in the more polar solvent from the resulting raflinate phase of the CNF compound having a lower number of NF groups dissolved in the hydrocarbon solvent, and recovering the CNF compounds separately from the extract solution and the raflinate phase solution.

3. The method of concentrating and separating higher NF adduct to an unsaturated organic compound having 4 NF groups attached to carbon atoms from a lower NF adduct of the unsaturated organic compound containing less than 4 NF groups attached to carbon atoms, which comprises contacting the mixture .of said adducts with a liquid hydrocarbon solvent for said adducts, contacting the solution of the said adducts in the hydrocarbon solvent having a dielectric constant of about 1.8 to 2.5 with a polyhalogenated organic liquid Which is immiscible with the liquid hydrocarbon solvent in a mixing zone, separating the resulting solution of said adducts in the polyhalogenated organic solvent as an extract from a raflinate 4 phase of the adducts in the hydrocarbon solvent, thereafter contacting said extract phase with a solution of the adducts in the hydrocarbon solvent with a solution of increased concentration of the higher adducts in the hydrocarbon solvent in an equilibration mixing zone to extract more of said higher adducts into the extract, and separating the resulting extract containing an increased amount of the higher adduct and decreased concentration of the lower adduct.

4. The method .of separating tetrakis(NF furan adduct from bis(NF furan adduct, which comprises contacting a benzene solution of said adducts with a more polar perfiuoro 3,4-dimethy1 hexane solvent to extract a higher proportion of the tetrakis adduct than of the bis adduct, and in the more polar solvent immiscible with the benzene, separating the resulting extraction from the =benzene solution and recovering the tetrakis adduct from the more polar solvent extract.

No references cited.

NICHOLAS S. RIZZO, Primary Examiner.

C. D. QUARFORTH, L. R. VERTIZ, Examiners.

L. A. SEBASTIAN, I. W. WHISLER,

Assistant Examiners. 

4. THE METHOD OF SEPARATING TETRAKIS (NF2) FURAN ADDUCT FROM BIS (NF2) FURAN ADDUCT, WHICH COMPRISES CONTACTING A BENZENE SOLUTION OF SAID ADDUCTS WITH A MORE POLAR PERFLUORO 3,4-DIMETHYL HEXANE SOLVENT TO EXTRACT A HIGHER PROPORTION OF THE TETRAKIS ADDUCT THAN OF THE BIS ADDUCT, AND IN THE MORE POLAR SOLVENT IMMISCIBLE WITH THE BENZENE, SEPARATING THE RESULTING EXTRACTION FROM THE BENZENE SOLUTION AND RECOVERING THE TETRAKIS ADDUCT FROM THE MORE POLAR SOLVENT EXTRACT. 